Molecular Design Strategy for Practical Singlet Fission Materials: The Charm of Donor/Acceptor Decorated Quinoidal Structure

Singlet fission (SF) has attracted much attention on account of its great potential for applications in high efficiency solar energy conversion. The major roadblock to realize this potential is rooted in the limited availability of practical SF material with strong absorption, suitable triplet energy level, an efficient SF process, and good chemical stability. Quinoidal structures feature an innate diradical character, which endows these skeletons with SF potential yet results in some structural instability. Herein, we propose a novel molecular design strategy for practical SF materials based on donor/ acceptor decorated quinoidal structures. This design strategy could allow the quinoidal structures to afford strong absorption, suitable energy levels, efficient SF properties, and excellent stability. Using transient spectroscopy techniques and theoretical simulation, a new SF chromophore based on a para-azaquinodimethane skeleton (AQTT) was successfully developed via the proposed design strategy. An ultrafast SF process, 165% triplet yield, suitable triplet energy of similar to 1.1 eV, strong visible-light-absorption coefficients similar to 10(5) M(-1)cm(-1), and good chemical stability make such material a promising SF candidate for practical photovoltaic applications.